It is believed that Generation Z's distinctive characteristics tend to challenge educators and employers in their organizations. To understand this cohort's traits or behaviors and know how to support this generation are key to the effectiveness of teaching, learning and collaboration with other generations. This study therefore aimed at discovering the personality traits of Gen Z undergraduates in Thailand by employing a mixed-method design. The participants in the study comprised 400 Gen Z undergraduate students at a university in Bangkok, Thailand. They were asked to respond to a questionnaire on a 4-point Likert's scale, which was developed based on the Big Five model (Goldberg, 1976) consisting of the 5 dimensions of personality: neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness. Tech-addiction has been proposed as another dimension of the model due to the prevalence of technology and social media at the present time. Likewise, a focus group interview with 5 students and semi-structured interviews with 4 EFL teachers were conducted. The findings revealed that of the six-personality dimensions, agreeableness was rated at the highest level whereas neuroticism was rated lowest. The personality traits of Gen Z seem to challenge educators in terms of classroom management and activity design. The implications of the study may contribute to EFL classroom practice.